1. Technical Field
The invention relates to the art of tire inflation systems for heavy-duty vehicles such as tractor-trailers or semi-trailers. More particularly, the invention relates to a rotary union for use in a tire inflation system for heavy-duty vehicles. Still more particularly, the invention is directed to a rotary union that is integrated into the interior of a hub cap of a wheel end assembly, which simplifies installation of the rotary union and reduces potential damage to the rotary union, thereby extending the life of the rotary union.
2. Background Art
Reference herein is made to tractor-trailers and semi-trailers by way of example, with the understanding that such reference applies to other heavy-duty vehicles, such as straight trucks. All tractor-trailers include at least one trailer, and sometimes two or three trailers, all of which are pulled by a single tractor. Each trailer includes a frame, from which at least one axle is suspended. A wheel end assembly is rotatably mounted on each end of the axle. More specifically, each wheel end assembly typically includes a wheel hub rotatably mounted on a bearing assembly that in turn is immovably mounted on a respective one of each of the ends of the axle, commonly known as an axle spindle. In this manner, the bearing assemblies enable each wheel hub to rotate about a respective axle spindle. A tire is, in turn, mounted on the wheel hub in a manner well known to those having skill in the art.
For normal operation of the wheel end assembly to occur, the bearing assembly and surrounding components must be lubricated with grease or oil. Therefore, the wheel end assembly must be sealed to prevent leakage of the lubricant, and also to prevent contaminants from entering the assembly, both of which could be detrimental to its performance. To seal the wheel end assembly, a hub cap is mounted on an outboard end of the wheel hub, and a main seal is rotatably mounted on an inboard end of the hub and the bearing assembly in abutment with the axle spindle, thereby creating a closed or sealed wheel end assembly.
Turning now to the tires that are mounted on the wheel hub, each trailer typically includes eight or more tires, each of which is inflated with air. Optimally, each tire is inflated to a recommended pressure that is usually between about 70 pounds per square inch (psi) and about 130 psi. However, it is well known that air may leak from a tire, usually in a gradual manner, but sometimes rapidly if there is a problem with the tire, such as a defect or a puncture caused by a road hazard. As a result, it is necessary to regularly check the air pressure in each tire to ensure that the tires are not under-inflated. Should an air check show a tire that is under-inflated, it is desirable to enable air to flow into the tire to return it to an optimum tire pressure.
The large number of tires on any given trailer setup makes it difficult to manually check and maintain the optimum tire pressure for each and every tire. This difficulty is compounded by the fact that multiple trailers in a fleet may be located at a site for an extended period of time, during which the tire pressure might not be checked. Any one of these trailers might be placed into service at a moment's notice, leading to the possibility of operation with under-inflated tires. Such operation may increase the chance of failure of a tire in service or may lead to less efficient operation of the vehicle as compared to operation with tires in an optimum inflation range.
Moreover, should a tire develop a leak, for example, as a result of striking a road hazard, the tire could fail if the leak continues unabated as the vehicle travels over-the-road. The potential for tire failure often is more pronounced in vehicles such as tractor-trailers that travel for long distances and/or extended periods of time.
As a result of such concerns, systems known in the art as tire inflation systems were developed. Tire inflation systems attempt to automatically monitor the pressure in a vehicle tire and/or inflate the vehicle tire with air to a minimum tire pressure as the vehicle is moving. Many of these automated systems utilize rotary unions that transmit air from a pressurized axle or air line to the rotating tires. The rotary union thus provides the interface between static components and the rotating wheel components. As a result, a rotary union typically is mounted in or near the outboard end of an axle spindle, and is fluidly attached to an outgoing air line which pneumatically connects to its respective tire proximate the axle spindle. Rotary unions of the prior art consist primarily of two designs, each of which exhibits disadvantages.
The first type of prior art rotary union is mounted in the outboard end of an axle spindle. These rotary unions have an outgoing air line that must exit the hub cap that seals the outboard end of the wheel end assembly. As the air line exits the hub cap, an elbow fitting or a tee fitting is often employed to enable the outgoing air line to extend to one or two tires mounted on that axle spindle. The elbow or tee fitting is attached to the exterior of the hub cap, which increases the possibility that the fitting can be damaged. Such damage may undesirably compromise the integrity of the tire inflation system, and/or may at least create a need to replace the fitting and other components of the system. To reduce the possibility of such damage, a guard typically is installed to protect the elbow or tee fitting, which results in increased cost and weight, and adds an additional component that must be removed and replaced when servicing the components of the wheel end assembly or the tire inflation system.
The second type of prior art rotary union is mounted on the exterior of the hub cap. These rotary unions include an outgoing air line that extends to the tire, and an inboardly-extending air tube which extends from the body of the rotary union, through the hub cap and into the axle spindle. During installation of such exterior rotary unions, the inboardly-extending air tube can be misaligned, resulting in premature wear of the bearings of the rotary union, which undesirably shortens the life of the rotary union. In addition, the mounting of the rotary union on the exterior of the hub cap causes the rotary union itself to extend outboardly of the hub cap, thereby increasing the possibility that the rotary union may undesirably be damaged and require replacement.
As a result, the potential damage and misalignment that are associated with prior art rotary unions makes it desirable to develop a rotary union that overcomes such disadvantages. The present invention satisfies these needs by providing a rotary union that is integrated into the interior of a hub cap, thereby simplifying and improving installation of the rotary union, and protecting the rotary union from damage.